In general, a scroll compressor includes in a casing a compressor mechanism including a first scroll having an end plate and a spiral wrap formed thereon and a second scroll having an end plate and a spiral wrap formed thereon and engaging with the first scroll. Usually, the first scroll is a stationary scroll which is prohibited from revolving in the casing and the second scroll is a moving scroll which is driven by a drive shaft to revolve about the drive shaft with a certain turning radius. In the scroll compressor, the moving scroll revolves about the drive shaft to vary the capacity of a compressor chamber defined between the stationary scroll and the moving scroll, thereby compressing gas such as refrigerant.
As an example of the above-described scroll compressor, Japanese Unexamined Patent Publication No. H8-334094 describes a scroll compressor including a position adjustment means for adjusting the position of one of the stationary and moving scrolls along the axial direction of the compressor mechanism. In the scroll compressor, the position adjustment means is configured to change the relative position of the scrolls between a compression position at which the wraps of the scrolls are in sealed contact with each other to define a compressor chamber therebetween and a non-compression position at which the wraps are not in the sealed contact. The scroll compressor is driven with the scrolls always at the compression position to work at 100% capacity. The scroll compressor is also able to work at a capacity less than 100% by intermittently shifting the scrolls to the non-compression position.
In the scroll compressor described in Japanese Unexamined Patent Publication No. H8-334094, an electromagnetic valve is used as the position adjustment means for making either one of a high pressure path and a low pressure path, both of which are connected to a chamber formed at the front side of the stationary or moving scroll, communicate with the chamber, thereby applying high or low pressure to the stationary or moving scroll. The scrolls are pressed against each other when the high pressure is applied, while they are separated when the low pressure is applied. For example, the chamber may be space inside a seal ring which is pressed against the bottom surface of the moving scroll (back pressure space).